Geomagnetically induced currents (GIC) carry information about near space phenomena, which is of NASA science interest. GIC can be harmful to the power grid and thus the information is valuable also for the transmission system operators.
When magnetic fields move about in the vicinity of a conductor such as a high-voltage power transmission line, a GIC is produced in the conductor. This happens on a large scale during geomagnetic storms on practically all long transmission lines. Long power transmission lines, for example, of many kilometers in length, are subject to damage by the GIC effect, especially in more modern high-voltage, low-resistance lines.
The nearly direct currents induced in high-voltage power transmission lines from geomagnetic storms are harmful to electrical transmission equipment, especially transformers. Such induced currents can induce core saturation, constrain transformer performance, trip various safety devices, and cause coils and cores to heat up. In some cases heat generated can disable or destroy a transformer, or even induce a chain reaction that can overload transformers throughout a system. A faulty transformer can also affect a linked generator by acting as an unbalanced load to a generator, causing negative sequence current in the stator and consequently heating of the rotor.